February 2016

Why Thinner Gasket Material Usually Works Better

Gasket materials come in many thicknesses. To give one example, at Hennig Gasket neoprene gasket material is available from 3/32” all the way up to 2” thickness. Customers will sometimes ask what thickness they should buy, but a gasket material supplier really can’t help with that. It depends completely on the application. However, it’s generally agreed that a gasket should be as thin as possible, providing it still seals. There are four reasons. A thinner gasket:

1. Has greater blow-out resistance. Being thinner, the gasket present less area to the internal pressure, so is less prone to deformation and failure.

2. Has a lower leak rate. All gaskets will allow some quantity of fluid to pass through. This is just a natural function of their structure and the make-up of the fluid being constrained. (Anyone who’s ever tried piping helium knows how its small molecules let it escape from almost anywhere!) So the less gasket material that’s exposed to the fluid, the less will leak.

3. Retains fastener torque better. This stems from the creep relaxation characteristics of the gasket material. When there’s less thickness there’s less creep, (think of it happening on a percentage basis,) so more torque is retained.

4. Is less expensive. Material cost relates more to volume or weight than area, and thicker gaskets need more material. Secondly, thickness also influences cutting method and thicker materials could be more expensive to cut to shape. Neoprene gasket material 3/32” thick die cuts readily, but a thickness of 2” may call for a waterjet.

Note though that points 1 and 2 really only apply to situations where the gasket resists pressure, such as in pipelines. In no-pressure situations such as a gasket sealing around an electrical enclosure, the benefit is primarily Point 4 – cost.

All About the Gap

How thick a gasket should be depends entirely on the application. Remember that it’s purpose is to take up an uneven gap between two surfaces. The key is having enough thickness that the gasket compresses and fills the voids, but no more.

HVAC Sealing Material Primer

HVAC system seals and gaskets maintain efficiency by preventing the loss of heated and cooled air. Whether installing new ductwork, modifying an existing system, or just replacing worn out gaskets, it’s important to choose appropriate material. Many HVAC specialists consider neoprene gaskets the default choice, but it’s possible better performance could be achieved with EPDM or silicone gaskets.

HVAC Gasket Applications

Gaskets have three main roles in HVAC systems:

  • Sealing opening panels, flaps, and doors
  • Reducing transmission of motor or fan vibration
  • Allowing for thermal expansion and contraction


Almost every ducting system includes access doors and panels, along with dampers that close off airflow through “legs” of the system. To minimize closing forces, these need a soft material with good compressibility. Combined with appropriate thickness, such gaskets will also take up the dimensional variation and uneven edges inevitable in most systems.

Reducing Vibration Transmission

Fans and motors can cause a vibration in flat ducting that’s audible as a low hum. To avoid complaints from building tenants, incorporate gaskets at appropriate interfaces. The cellular structure absorbs the vibration and prevents it spreading throughout a system.

Expansion and Contraction

Metal ducting experiences significant dimensional changes in response to switching between warmed and cooled air. A gasket with good recovery takes up these changes while still maintaining a leak-tight seal.

Environmental Factors

Outdoor applications challenge HVAC gasket material as UV light degrades some materials, and moisture penetration must be avoided. Low temperatures and ozone might also be a concern in some applications.

HVAC Gasket Materials

Neoprene gaskets and those made from thermoplastic elastomers (TPE’s) generally perform when soft and resistant to compression set. EPDM gaskets work well outdoors as they stand up to sunlight and other weathering effects. Where air or gas temperatures are high silicone gaskets can be a good choice.

Closed cell materials may be preferable because air and moisture cannot pass through, although these are firmer, requiring higher closing forces.

Installation is simplified by using a pressure sensitive adhesive (PSA). This can be laminated on to the gasket material or can be applied in tape form.

Selecting Gasket Material: Consider Temperature Carefully

All gasket materials have a temperature range they work over. Going outside of this range is a recipe for leakage, but buying one with a wider range than is necessary can be unnecessarily expensive. Why buy a silicone gasket when a nitrile gasket will do the job? The key lies in understanding the expected in-service temperatures.

Effects on the joint

Temperature, and especially temperature cycling, affects sealing in three ways:

  • Expansion/contraction of the joint and fasteners alters clamping loads and gaps.
  • High/low temperatures can result in material cracking of extruding out of the joint.
  • Cycling demands the material recovers to maintain the seal at all times.

The external thermal environment

Gaskets placed outdoors can experience large temperature swings, but ambient temperature is only part of the story. Piping running above a desert floor will absorb solar energy, getting well above 100F. Likewise, a brisk north wind in a Minnesota winter can produce effective temperatures far below zero.

Extreme temperatures are not uncommon indoors either. Foundries and frozen food distribution centers are both examples of where gaskets could see very high or very low temperatures, (although swings between the two are less likely.)

Media temperature

Knowing the mean temperature of the media being transported or sealed isn’t enough. Abnormal operating conditions could lead to unexpected peaks or dips, as can shut-downs and start-ups. Steam cleaning in particular can lead to higher than normal temperatures.

For enclosures it’s important to estimate the worst-case thermal load. Electrical equipment like drives and transformers produce significant heat and while a cabinet might have ventilation, consider the possibility of a blocked filter or failed fan.

Thermal gradients

Temperature differentials across a sealed joint can also challenge gasket materials, especially when that gradient changes. Piping cryogenically-cooled liquids through the desert, or hot gases in the arctic can make joints move and needs materials that recover quickly without taking a compression set.

Consider the worst-case

When selecting gasket material, know what temperatures to anticipate and choose accordingly. For information on gasket materials, contact a product specialist at Hennig Gasket.